1. Field of the Invention
This invention relates in general to a tool holder for use on a numerically controlled machine tool. More particularly, it relates to such a tool holder which is capable of automatically adjusting or compensating the position of a cutting tool thereon by utilizing the rotation of a tool spindle receiving the tool holder.
2. Description of the Prior Art
Generally, boring tool holders, as used in numerically controlled boring machines, incorporate a tool position compensating mechanism therein. This compensating mechanism serves to adjust the position of a cutting tool, carried on the tool holder, in a radial direction thereof, so that it is possible either to machine bores of different diameters or to compensate the radial position of the tool for wear of the cutting edge of the tool.
One type of known tool holder incorporating such a tool position compensating mechanism receives an external sleeve at its circumferential surface, and tool position adjustment is performed by rotating the tool holder after rigidly holding the external sleeve by means of suitable rotation preventing means. However, the provision of the external sleeve disadvantageously causes the diameter of the tool holder to be increased, thus resulting in restrictions on the bores that can be machined by the use of the tool holder. The provision of the external sleeve further causes weight unbalance of the tool holder, thereby generating vibration during machining operations whereby the accuracy of bores machined by the use of the tool holder is degraded.